When creating a test, you can set the test goal as either sessions, profit or conversion rate. This option is largely used when deciding on when to end a test - when either the profits, sessions or conversion rate achieves statistical significance.
You should set the goal for the right test:
Always use profit when doing a pricing test. This is because the pricing may have an effect on conversions, but the higher/lower price can counteract that change in conversion rate.
This is particularly useful when trying to increase your ranking or click through rate. This goal can be used when testing the title or primary image.
For all other tests, we would recommend you set the goal of the test to conversion rate - simply because this metric is probably the most important (along with your profits). The higher the conversion rate, the higher your rankings in the long run. Amazon knows every click that does not result in a purchase is a wasted click, Amazon removes this wastage by putting products that have a low conversion rate to the bottom of the search results.
For a test to be fully optimised it is wise to perform a wide range of tests on all of the fields - this also means choosing the correct goal for the test.